I'm beginning with navigation components and I'm facing some problem with a livedata observer.
For example: I have this livedata, who manage auth response from server.
viewModel.authenticate.observe(this, Observer {
manageAuthResponse(it)
})
Everything works fine, and I go to Fragment B. But when I'm in Fragment B, and I try to go back to Fragment A (who contains that livedata), the Observer
fires again with the previous result (SUCCESS).
How can I prevent this?
When I go back, I want to refresh this result and prevent livedata observer to be fired.
Wrap your LiveData object in a ConsumableValue
like this
class ConsumableValue<T>(private val data: T) {
private var consumed = false
fun consume(block: ConsumableValue<T>.(T) -> Unit) {
if (!consumed) {
consumed = true
block(data)
}
}
}
then in viewmodel
val authenticate = MutableLiveData<Consumable<AuthenticationObject>>()
and in your fragment
viewModel.authenticate.observe(this, Observer { consumable ->
consumable.consume {
manageAuthResponse(it)
}
})
Wrap the LiveDate Like this
open class LiveEvent<T> : MediatorLiveData<T>() {
private val observers = ArraySet<ObserverWrapper<in T>>()
@MainThread
override fun observe(owner: LifecycleOwner, observer: Observer<in T>) {
val wrapper = ObserverWrapper(observer)
observers.add(wrapper)
super.observe(owner, wrapper)
}
@MainThread
override fun observeForever(observer: Observer<in T>) {
val wrapper = ObserverWrapper(observer)
observers.add(wrapper)
super.observeForever(wrapper)
}
@MainThread
override fun removeObserver(observer: Observer<in T>) {
if (observers.remove(observer)) {
super.removeObserver(observer)
return
}
val iterator = observers.iterator()
while (iterator.hasNext()) {
val wrapper = iterator.next()
if (wrapper.observer == observer) {
iterator.remove()
super.removeObserver(wrapper)
break
}
}
}
@MainThread
override fun setValue(t: T?) {
observers.forEach { it.newValue() }
super.setValue(t)
}
private class ObserverWrapper<T>(val observer: Observer<T>) : Observer<T> {
private var pending = false
override fun onChanged(t: T?) {
if (pending) {
pending = false
observer.onChanged(t)
}
}
fun newValue() {
pending = true
}
}
}
then in ViewModel
val viewModel = LiveEvent<Resource<String>>()
This solution is work for me
You can check out the code in this github
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